Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
  • A61L2/02—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using physical phenomena
  • A61L2/08—Radiation
  • A61L2/081—Gamma radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65B—MACHINES, APPARATUS OR DEVICES FOR, OR METHODS OF, PACKAGING ARTICLES OR MATERIALS; UNPACKING
  • B65B55/00—Preserving, protecting or purifying packages or package contents in association with packaging
  • B65B55/02—Sterilising, e.g. of complete packages
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2202/00—Aspects relating to methods or apparatus for disinfecting or sterilising materials or objects
  • A61L2202/20—Targets to be treated
  • A61L2202/24—Medical instruments, e.g. endoscopes, catheters, sharps

Definitions

• the present invention is directed to a novel process for sterilizing an article made from polymeric materials by radiation sterilization.
• the article is enclosed in an gas impermeable package together with an oxygen absorber for a time sufficient to consume substantially all of the oxygen in the package and the oxygen dissolved in the polymeric material.
• the article is preferably intended for medical use and may contain a radiation sterilizable parenterally administerable preparation.
• Sterilizing medical articles of polymeric materials can be performed by a number of methods, such as steam sterilization (autoclavation), radiation sterilization (electron beam (EB), ⁇ - and ⁇ -radiation), ethylene oxide (EtO) and aqueous formaldehyde.
• autoclavation autoclavation
• radiation sterilization electron beam (EB)
• EB radiation sterilization
• EtO ethylene oxide
• aqueous formaldehyde aqueous formaldehyde.
• a technical problem that requires especially careful consideration is the sterile packaging and storing of parenterally administerable fluids that both are sensitive to atmospheric oxygen during storage and incompatible with many polymeric materials and their additives.
• Oxygen absorbers have previously been successfully used for the packaging of oxygen sensitive medical fluids like amino acid solutions and fat emulsions.
• the absorbers have been positioned between an inner medical container made from a gas pervious polymer material filled with the medical solution and an outer enclosing sheet made of an gas impermeable material.
• Such packages are disclosed by e.g. the European patent specifications EP-A-0 093 796 and EP-A-0 510 687.
• Sterilization by irradiation is a desirable alternative method to heat sterilization, since it will provide a simpler and less costly manufacturing process. It is, however, a technique that must be carefully considered, because of the chemical and physical alterations that can be induced in the polymeric material in the presence of atmospheric oxygen.
• EP-B-0 218 003 discloses a radiation sterilized medical device enclosed in a gas permeable bag which is irradiated with ⁇ -radiation and thereafter placed in a gas impermeable wrapping member together with a deoxidizing agent. Both residual oxygen and ozone resulting from the gamma radiation will thereby be absorbed and because the entry of oxygen from the external environment is almost completely prevented, an oxygen-free condition within the wrapping is obtained.
• the purpose of the technique disclosed in EP 0 218 003 is primarily to prevent the "gamma"-odour associated with ozone.
• the British patent specification 1,230,950 describes a similar method of sterilizing material packaged together with an oxygen scavenger with ⁇ -radiation.
• the sterilizing methods according to these patent specifications may, however, lead to the formation of undesired and potentially deleterious degradation products originating from free radicals of the polymeric material and the small amounts of dissolved oxygen that remains in the polymeric material during the ⁇ -irradiation.
• the activity of the highly reactive free radical containing molecules may to a certain degree pervade the original polymeric structure of the material by bond cleavage and macroradical formation, thereby making the material discoloured or changing its mechanical properties.
• a layered polymeric material with adhered or built-in oxygen scavengers may at least partially the problems of secondary effects originating from dissolved residual oxygen in the material.
• the ⁇ -radiation will cause local overheating in the material that leads to thermal oxidation that destroys the oxygen scavengers.
• Hindered amines such as those based on 2,2,6,6,-tetramethylpiperidine operate as antioxidants at ambient temperatures in light-stabilization packages. Furthermore they and their products are colourless or only very weakly absorbing. These aliphatic amines have been previously shown to function as stabilizers to post- ⁇ -irradiation oxidation of polyolefines, a phenomenon explained on page 433, Chapter 26 "Stabilization of polyolefines to Gamma Irradiation" in the above cited D. J. Carlsson et al.
• the irradiated polyolefin will, due to the production of free radicals among other compounds form hydroperoxides, which may be decomposed under the formation of even more free radicals. Highly efficient stabilizer combinations might possibly suppress oxidation to the point where atypical hydroperoxide products dominate. Post-irradiation oxidation is largely dependent upon initiation by the slow thermal decomposition of the hydroperoxides. Hydroperoxide decomposition by an additive, such as hindered amines, will also prevent this oxidative degradation. However, in medical applications all such additives are generally avoided, since they tend to discolour the articles and may migrate from the material and consequently introduce a toxicity risk.
• the net result of irradiation is the composite result of reactions (5)-(9) so that crosslinked gel or a degradation of molecular weight results.
• the behaviour of various polymers irradiated in the absence of oxygen may be generalized into those which crosslink during irradiation; polyethylene, poly(methyl acrylate), poly(acrylic acid), polystyrene) and those which degrade (poly(methyl methacrylate), poly(methacrylic acid), poly( ⁇ -methylstyrene), poly(butene-2).
• Polypropen undergoes both scission and crosslinking.
• Crosslinking increases the stiffness of plastics and can render them inextensible.
• Poly(olefin sulphones) have been shown to be exceptionally sensitive to ⁇ - or electron-beam radiation and can be used as short-wavelength photoresists. Chain scission also leads to embrittlement, but the effect of direct, radiation-induced scission in commodity polymers is normally minor compared with oxidative chain scission.
• alkoxyl radicals are formed by hydroperoxide decomposition. ##STR6## They are also formed in the complex self-reaction of peroxyl radicals which may terminate the radicals. Elongation at break has been shown to be appreciably more sensitive to degradation than tensile strength.
• the radiation sensitivity of polymeric materials is generally affected by impurities, additives, dose rate, sample thickness and morphology.
• the highly oriented, chain-extended morphology in highly drawn PE fibres is much more ⁇ -irradiation-resistant than the usual melt-quenched semicrystalline morphology. This results both from restricted O 2 diffusion and effects on radical decay rates. It is therefore complicated to predict the marked effect of the dose rate.
• a purpose with the present invention is also to obtain a safe and reproducible sterilization of sensitive medical objects without being dependent on expensive methods like evacuating air and introducing inert gases and steam sterilisation.
• the invention is related to a process for sterilizing an article comprising a polymeric material by means of radiation, wherein the said polymeric material is enclosed in a gas impermeable package together with an oxygen scavenger containing a supply of water for a time sufficient to consume substantially all of the oxygen in the package, and also the oxygen dissolved in the matrix of the polymeric material.
• the package and its content is thereafter subjected to a sterilizing dosage of ⁇ -radiation.
• the article is preferably for medical use, but also other sensitive instruments and/or electronic articles are conceivable to sterilize, if they are compatible with ⁇ -radiation.
• the article to sterilize is a container made from a polymeric material filled with a radiation sterilizable product, wherein both the container and its content is subjected to the said process.
• the product is preferably a parenterally administerable medical preparation, but other products like nutrients are also possible to sterilize in this manner.
• An important part of the present invention is the use of a water containing oxygen scavenger for removing substantially all oxygen dissolved in the matrix of a polymeric object that shall be subjected to sterilization by ⁇ -radiation.
• a suitable oxygen scavenger which is more detailly described below, is iron oxide based and contain crystalline water, but other deoxidizers are also conceivable.
• Also parts of the present invention are a gamma-radiation sterilized medical article made of a polymeric material and a gamma-radiation sterilized container made of a polymeric material containing a radiation sterilizable medical product intended for parenteral administration, both produced by the mentioned process.
• the polymeric material or the filled container made thereof is stored a predetermined suitable time period in a gas permeable enclosure or package together with the oxygen scavenger in order to consume substantially all oxygen, even the oxygen molecules dissolved in the polymeric matrix of the article.
• a suitable storage period of the article made of polymeric material together with the oxygen scavenger is from at least about 48 hours to several weeks. A number of factors will influence the length of the storage period, among which the most important is the chemical nature of the polymer and its affinity to the oxygen molecules, the capacity of the oxygen absorber, the number (or quantity) of absorbers and the volume enclosed by the gas impermeable package.
• Typical oxygen absorbers useful in the present invention will have a capacity of absorbing about 10 to 15 ml oxygen per hour. With the knowledge about the initial oxygen content of enclosed atmosphere, the kinetics of the absorber and the specific oxygen affinity of the polymeric material, an estimation of the storage time period to obtain substantially oxygen free conditions can be made for each system. It must also be considered to be within the inventive concept to find out suitable relations between storage time, characteristics and amount of the polymeric material and the amount and distribution of the oxygen scavenger present in the gas impermeable package. Suitable storage times to obtain substantially oxygen free conditions also within the matrix of the polymeric material will vary from about 48 hours to several weeks.
• the said polymeric material can be a homogenous composition or be various mixtures including multilayered polymeric sheet materials. At least one polymer should belong to the category that can be secondarily oxidized and cross-linked as defined above.
• the invention will be especially advantageous if the material includes polypropen and/or polyethylene, but anyone skilled in the art can find numerous alternatives.
• the gas impermeable package preferably contains an aluminium layer or consists of an aluminium foil.
• suitable materials are PVDC, EVOH, PVOH, plasma coated multilayered structures containing SiO x , Al 2 0 3 etc., certain aromatic nylons, such as MXD-6 and the multilayered structures in the international patent application PCT/SE94/00138.
• the gas impermeable package containing the polymeric medical article or the polymeric container filled with a product for parenteral administration can optionally be sealed in an oxygen depleted atmosphere in the presence of nitrogen or another suitable inert gas.
• An important advantage of the invention is the possibility of sealing the gas impermeable package in air, without the use of inert gases, and still be able to obtain an advantageous ⁇ -radiation sterilization without side reactions.
• the container that is filled with a product for parenteral administration is preferably made of EVOH, polypropen, polyethylene, EVA, Excel®, Nylon-11 or other polymeric materials which are partially gas permeable.
• the filling and sealing procedure of the container is performed with conventional aseptic procedures and will not be further discussed herein.
• the invention is applicable on a wide range of polymeric materials and parenterally administerable products.
• Especially preferred products are such intended for parenteral administration that must be stored after production and which contains high amounts of oxygen sensible and/or heat sensitive amino acids, proteins or lipid emulsions comprising sensitive unsaturated fatty acids.
• Such products can be stored either in fluid form or as dry powder in different compartments of a container together with an equally sterilized solvent that just before administration are reconstituted to a parenterally administerable liquid composition.
• a suitable oxygen absorber is enclosed in a small bag and is used as a desiccant.
• Such oxygen absorbers are well known from the food industry and they are placed in a package of food to remove oxygen and prevent the food from deterioration due to the oxygen present. The food maintains its original taste, as there is no growth of mould and no progress of oxidation.
• the latter type is preferably utilized in the present invention in combinations with a gas impermeable overwrap and a polymer material that is exposed to ⁇ -irradiation.
• the former type can be used if water is supplied together with the oxygen absorber.
• Oxygen absorbers composed of iron powder are especially preferred according to the present invention. They are based on the fact that rusting of iron requires oxygen. The oxidation mechanism is too complicated to be expressed by a single formula, but can generally be expressed as follows.
• the doses of gamma-radiation used in the present invention are of a conventional magnitude with a dose rate of about 0.1 Mrad/hr and the irradiation doses of about 15 to 35 kGy.
• the investigated compound is a polypropen/Kraton mixture in a shape of 1 mm thick saddle-port system adjusted with an injection-port in natural rubber (latex).
• the trade name of the polypropen is Fina Dypro Z-7650, processed by Fina
• the trade name of the Kraton is Kraton G-1652, processed by Shell.
• the two materials are compounded by Ferro.
• An iron-based scavenger ZR-200, processed by Mitsubishi, is used when an oxygen free material shall be obtained and nitrogen when an oxygen free atmosphere shall be obtained.
• Gamma radiation was performed by using a Cobalt-60 isotope with a dose rate of 0.1 Mrad/hr.
• the irradiation dose was 35 kGy.
• the irradiated saddles were visually inspected directly after irradiation.
• the degree of visual discolouration of the polypropylene/Kraton material and the visual damage of the rubber injection-port were evaluated.
• a non-irradiated polypropylene/Kraton saddle was studied.
• the properties of polymeric materials are affected by radiation as a result of the chemical changes in the polymer molecules.
• the PP/Kraton material has become yellow and the rubber injection-port has been damaged.
• an absorber, ZR-200 this colour change of the material does not occur and no visual damage of the rubber injection-port has been seen.
• Table 2 shows FTIR peak height indexes of polypropylene/Kraton samples, non-irradiated and irradiated in different atmospheres with a dose of 35 kGy gamma-radiation.
• the peak heights at 1750, 1650 and 1150 cm -1 are all compared with the peak height at 1460 cm -1 .
• Table 3 shows tensile strength and elongation at break of the aforedescribed samples.
• the Tensile-Strain testing before and after irradiation was carried out at 25° C. using rectangular shaped test pieces (10 * 55 mm) with a thickness of 1 mm.
• An Universal Testing Machine, Model Alwetron TCT5 was used at a crosshead speed of 500 mm/min.
• Chemiluminiscence is a method to measure photons emitted during the decay of hydroperoxides.
• Fast Chemiluminiscence analysis was studied with a commercial Thermo Luminescence Dosimeter (TLD) from Alnor Instruments AB. With the TLD the number of photons emitted from irradiated and non-irradiated Polypropylene/Kraton samples was determined.
• the Chemiluminiscence analysis was performed under nitrogen atmosphere at 100° C. or 130° C. for 70 s.
• Table 4 shows chemiluminiscence at 100° C. and Table 5 at 130° C.
• Mettler TA 3000 consisting of a microbalance Mettler MT5 and a furnace controlled by a TC 10 A processor
• the loss of mass of the polypropylene/Kraton material was measured as a function of time.
• Ca 35 mg sample was heated from room temperature to 600° C. with a heating speed of 5° C./min. Irradiated and non-irradiated samples were analysed.
• a Mettler TA 3000 system was used with a Differential Scanning Calorimetry measuring cell DSC 30 and a processor TC 10A. Ca 20 mg samples were heated from -100° C. to 300° C. at a heating rate of 10° C./min under nitrogen atmosphere. Irradiated and non-irradiated samples were analysed.
• the increase in melting temperature, compared to the non-irradiated sample, of the PP is due to crosslinking and decrease in ⁇ H, compared to the non-irradiated sample, indicates a reduction in crystallinity of the material due to the formation of crosslinking when irradiated air.
• samples were analysed by head space GC-MS.
• the analysis apparatus consisted of a GC model Hewlett Packard 5890 equipped with a mass detector 5972 and a head space sampler 7694. The samples were heated at 130° C. for 60 minutes before transferred to the GC apparatus. As column in the GC separation a HP Ultra 2,50 m * 0.32 mm was used. The temperature programme used was the following; 60° C. for 10 min, 10° C./min up to 230° C., injection temperature: 220° C.
• the unknown compound that exists as degradation compound is probably from an aromatic antioxidant of the PP material.
• the material irradiated in the presence of an oxygen absorber has the same degradation compounds as the non-irradiated sample which is of major importance.
• the test demonstrates how potentially toxic degradation products like cyclohexene, cyclohexanol and cydohexanon are absent in the samples which have been irradiated in the presence of an oxygen absorber.

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• Health & Medical Sciences (AREA)
• Veterinary Medicine (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Epidemiology (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Apparatus For Disinfection Or Sterilisation (AREA)
• Food Preservation Except Freezing, Refrigeration, And Drying (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Polyesters Or Polycarbonates (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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Cited By (64)

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Citations (16)

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• 1994
  • 1994-06-08 SE SE9401986A patent/SE9401986D0/xx unknown
• 1995
  • 1995-06-08 JP JP8500775A patent/JPH10501204A/ja not_active Ceased
  • 1995-06-08 AT AT95922067T patent/ATE237505T1/de not_active IP Right Cessation
  • 1995-06-08 ZA ZA954735A patent/ZA954735B/xx unknown
  • 1995-06-08 US US08/750,245 patent/US5881534A/en not_active Expired - Fee Related
  • 1995-06-08 EP EP95922067A patent/EP0759873B1/de not_active Expired - Lifetime
  • 1995-06-08 AU AU26884/95A patent/AU690697B2/en not_active Ceased
  • 1995-06-08 DK DK95922067T patent/DK0759873T3/da active
  • 1995-06-08 WO PCT/SE1995/000684 patent/WO1995033651A1/en active IP Right Grant
  • 1995-06-08 CA CA002192365A patent/CA2192365C/en not_active Expired - Fee Related
  • 1995-06-08 DE DE69530386T patent/DE69530386T2/de not_active Expired - Fee Related

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